[libdispatch-dev] libdispatch for Win32

[DrPizza]

FYI, my code is available at:
https://github.com/DrPizza/libdispatch


From: Marius Zwicker [mailto:marius at mlba-team.de]
Sent: 23 April 2011 06:42
To: DrPizza
Cc: libdispatch-dev at lists.macosforge.org
Subject: Re: [libdispatch-dev] libdispatch for Win32


Hey Peter,

It is great to discover that much interest into porting libDispatch to Windows lately. As you might have read while browsing the archives of this mailing list, I am working on a win32 port as well - and have already done just the same as you did. Thanks to the help of Brent Fulgham we can build on MSVC as well. The idea of using C++0x lambdas as a workaround for missing blocks support occured to me too - seems as if the number of similarities between our two ports is not going to end soon.

As such I would consider it odd if we spent time and energy (as already happened far too much) into maintaining and developing two windows variants of libdispatch. I'd love to merge our two source trees, just have a look at mine by going to http://opensource.mlba-team.de/svn/xdispatch/trunk/core/ or opensource.mlba-team.de/xdispatch for more excessive documentation. I - too - have concurrent and serial queues working and I am currently fixing the timers on windows. Please note my annotations to your ideas below.

Sincerely, Marius



> On Sat, 23 Apr 2011 03:07:19 +0000, DrPizza wrote:

> So, I've got the basics working tolerably well. Is this something that people

> care about/want source for?



> What I've done so far is as follows:



> Get most of the code building properly in VC++ 2010:

>  * Replace C99 named initializers with old-fashioned aggregate initializers.

>  * Replace gcc typeof with real type names.

>  * Replace gcc's fancy macros with less fancy standard C89 ones.

>  * VC++ has no equivalent (AFAIK) to gcc's transparent_union, so insert

>    casts as necessary.
> * Minor bits and pieces like get rid of the ?: gccism.

>  * Provide minimal Win32 equivalents to missing UNIX headers that seem

>    necessary.

Please see the shims folder within my source tree

> Blocks:

>  * Only Microsoft is in a position to produce built-in block support for

>    VC++ and I'm sure as hell not going to write a source-source translator.

>    Instead, I have a C++ lambda wrapper that works in conjunction with the

>    _f function variants. This seems more than enough for most purposes.

I moved my lambda implementation into xdispatch, in order to keep libdispatch
as pure c library. It really seems to work well.

> Port pthread_workqueues to Win32:

>  * Built on top of "new-style" (Vista and up) Win32 threadpools.

>  * Reasonably complete.

>  * Reasonably inadequately tested.

Is there a reason for you not using the readily ported libpthread_workqueue of Mark Heily? By using
the older style threadpool you can achieve a broader compatibility as windows xp still seems quite familiar among users.

> Rework dispatch_sources:

>  * The Windows overlapped I/O model is better than the traditional UNIX one,

>    but doesn’t readily support:

>        DISPATCH_SOURCE_TYPE_READ

>        DISPATCH_SOURCE_TYPE_WRITE

>  * And Windows in general doesn't have any good analogues to:

>        DISPATCH_SOURCE_TYPE_VNODE

>        DISPATCH_SOURCE_TYPE_SIGNAL

>        DISPATCH_SOURCE_TYPE_PROC

>        DISPATCH_SOURCE_TYPE_MACH_RECV

>        DISPATCH_SOURCE_TYPE_MACH_SEND

>  * But what I do have instead is initial support

>        DISPATCH_SOURCE_TYPE_OIO (for "overlapped I/O")

>            example: https://gist.github.com/938097

>  * Overlapped I/O supports files, sockets, named pipes, and more. All of

>    these need testing.

>  * The loss of READ/WRITE/SIGNAL/MACH_* is no big deal on Windows, as they

>    don't really fit into Win32 anyway. Only one PROC feature (EXIT)

>    translates into Win32, and I'm not seeing any clearly compelling reason

>    to replicate it, as it doesn't seem especially useful. However, the loss

>    of VNODE is unfortunate, as it both have interesting features. But this

>    may not be fatal. ReadDirectoryChangeNotificationsW supports overlapped

>    I/O, so should plumb into my existing DISPATCH_SOURCE_TYPE_OIO with no

>    changes anyway, though the interface will not be quite as tidy.

>  * I still need to test:

>        DISPATCH_SOURCE_TYPE_DATA_ADD

>        DISPATCH_SOURCE_TYPE_DATA_OR

>  * I need to fix:

>        DISPATCH_SOURCE_TYPE_TIMER

>    I ripped out part of the machinery to make the code clearer temporarily;

>    now I need to add it back.

>  * I also need to examine the ins and outs of cancellation and suspension

>    and so on and so forth. Win32 doesn't allow a handle to be detached from

>    an IOCP except by closing the handle, so there are some sadnesses there.

>    I'm not sure how much impact they'll have in practice, possibly none.

>  * I am toying with the idea of something along the lines of

>    DISPATCH_SOURCE_TYPE_WAITABLE, which would perform a wait on any Win32

>    waitable object (so mutex, event, waitable timer handles, amongst others)

>    and dispatch a message to a queue when that wait occurs. This would give

>    us back the one PROC scenario that makes sense in Win32, too, as you can

>    wait on a process handle, and the wait resumes when the process

>    terminates. Due to the annoying traits of WaitForMultipleObjects (it's

>    limited to 64 HANDLEs), however, this might be a little awkward to

>    implement without moving to a rather wasteful thread-per-wait model.

>  * There are almost certainly memory leaks, bugs, etc.. My focus has been on

>    validating the general approach more than writing a bunch of test cases.

Did you re-implement your own version of kqueues or completely exchange the kevent etc. calls
within your source code? DISPATCH_SOURCE_TYPE_OIO sounds interesting, as Mark and I already
discussed a similar solution "as the way to go" on windows.

> Main queues:

>  * From my understanding of Mac OS X, Windows has no real meaningful

>    equivalent of Cocoa's blessed main queue. Any thread can have a message

>    pump and associated windows, which it's then responsible for drawing,

>    etc.. Processes have an M:N model (M threads, controlling N windows),

>    with each window being affinitized to its own thread.

>  * However, the ability to post a message back into a window's message loop

>    is obviously invaluable, so I want to create as close a workalike as

>    makes sense in Win32. Something that captures the spirit, if not the

>    exact same API. I've not yet written any code for this, but my plan of

>    action is to do something along these lines:

>        1) allow creation of serial queues bound to an HWND or HWNDs.

>           Callbacks posted to these queues will be pumped into the WndProc

>           one-by-one.

>        2) Either a WndProc hook or a helper function (or both) to respond to

>           the callbacks posted to the WndProc and execute them.

>        3) Possibly some convenience helpers to allow the retrieval of a

>           queue given an HWND and so on.

> Distant future:

>  * There would be certain benefits to ripping out the pthread_workqueues and

>    using the new-style Win32 threadpools directly. The Win32 threadpools

>    directly support timers, so they might allow DISPATCH_SOURCE_TYPE_TIMER to

>    be moved off the dispatch_mgr queue/thread. Likewise, they directly

>    support overlapped I/O, so might allow DISPATCH_SOURCE_TYPE_OIO to be

>    moved off the dispatch_mgr thread too. They also directly support

>    waits on handles, which would greatly simplify

>    DISPATCH_SOURCE_TYPE_WAITABLE (if I do indeed go down that route).

>    So the advantages would be many--but I am wary of diverging too far from

>    the existing source, which is why thus far I've implemented

>    pthread_workqueues instead; it was the easy solution.
> * Going in the opposite direction, some might prefer switching to Windows

>    2000-style thread pools, so as to support Windows XP instead. This would

>    work (and I think someone on the list mentioned that they had implemented

>    pthread_workqueue on that API already), but it also means eliminating the

>    possibility of the streamlined implementations described above.

I have to disagree. By using RegisterWaitForSingleObject on a timer handle you can
easily achieve similar behaviour using the "old" thread pool api without needing an
additional manager thread.

> Source code:

>    My plan was to dump it into my github, if people find the whole thing

>    interesting, though I was going to wait until I'd fixed timer sources,

>    since they're rather important.

>

> Peter
>

That would be interesting although I hope we can merge our efforts within the near
future.
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